One of the major nuisances of C++ compared to other languages is the manual
management of #include directives in any file.
clang-include-fixer addresses one aspect of this problem by providing
an automated way of adding #include directives for missing symbols in one
translation unit.

While inserting missing #include, clang-include-fixer adds
missing namespace qualifiers to all instances of an unidentified symbol if
the symbol is missing some prefix namespace qualifiers.

To use clang-include-fixer two databases are required. Both can be
generated with existing tools.

Compilation database. Contains the compiler commands for any given file in a
project and can be generated by CMake, see How To Setup Tooling For LLVM.

Symbol index. Contains all symbol information in a project to match a given
identifier to a header file.

Ideally both databases (compile_commands.json and
find_all_symbols_db.yaml) are linked into the root of the source tree they
correspond to. Then the clang-include-fixer can automatically pick
them up if called with a source file from that tree. Note that by default
compile_commands.json as generated by CMake does not include header files,
so only implementation files can be handled by tools.

The include fixer contains find-all-symbols, a tool to create a
symbol database in YAML format from a compilation database by parsing all
source files listed in it. The following list of commands shows how to set up a
database for LLVM, any project built by CMake should follow similar steps.

This enables clang-include-fixer for NORMAL and VISUAL mode. Change
<leader>cf to another binding if you need clang-include-fixer on a different
key. The <leader> key
is a reference to a specific key defined by the mapleader variable and is bound
to backslash by default.

Make sure vim can find clang-include-fixer:

Add the path to clang-include-fixer to the PATH environment variable.

Or set g:clang_include_fixer_path in vimrc: letg:clang_include_fixer_path=path/to/clang-include-fixer

You can customize the number of headers being shown by setting
letg:clang_include_fixer_maximum_suggested_headers=5

Customized settings in .vimrc:

letg:clang_include_fixer_path="clang-include-fixer"

Set clang-include-fixer binary file path.

letg:clang_include_fixer_maximum_suggested_headers=3

Set the maximum number of #includes to show. Default is 3.

letg:clang_include_fixer_increment_num=5

Set the increment number of #includes to show every time when pressing m.
Default is 5.

letg:clang_include_fixer_jump_to_include=0

Set to 1 if you want to jump to the new inserted #include line. Default is
0.

letg:clang_include_fixer_query_mode=0

Set to 1 if you want to insert #include for the symbol under the cursor.
Default is 0. Compared to normal mode, this mode won’t parse the source file
and only search the sysmbol from database, which is faster than normal mode.

To run clang-include-fixer on a potentially unsaved buffer in Emacs.
Ensure that Emacs finds clang-include-fixer.el by adding the directory
containing the file to the load-path and requiring the clang-include-fixer
in your .emacs:

Within Emacs the tool can be invoked with the command
M-xclang-include-fixer. This will insert the header that defines the
first undefined symbol; if there is more than one header that would define the
symbol, the user is prompted to select one.

To include the header that defines the symbol at point, run
M-xclang-include-fixer-at-point.

Make sure Emacs can find clang-include-fixer:

Either add the parent directory of clang-include-fixer to the PATH
environment variable, or customize the Emacs user option
clang-include-fixer-executable to point to the file name of the program.

To get the most information out of Clang at parse time,
clang-include-fixer runs in tandem with the parse and receives
callbacks from Clang’s semantic analysis. In particular it reuses the existing
support for typo corrections. Whenever Clang tries to correct a potential typo
it emits a callback to the include fixer which then looks for a corresponding
file. At this point rich lookup information is still available, which is not
available in the AST at a later stage.

The identifier that should be typo corrected is then sent to the database, if a
header file is returned it is added as an include directive at the top of the
file.

Currently clang-include-fixer only inserts a single include at a
time to avoid getting caught in follow-up errors. If multiple #include
additions are desired the program can be rerun until a fix-point is reached.